Polyester films have been used in various applications, such as materials of magnetic recording media, electrical insulators, solar cells, capacitors and packagings and industrial materials, by taking advantage of their characteristics such as excellent mechanical, thermal and surface properties as well as excellent heat resistance. In recent years, among these applications, the demand for solar cells that generate clean energy as semi-permanent and pollution-free next-generation energy source has increased, and polyester films have been used as a member constituting a solar cell backsheet (Patent Documents 1 and 2). In addition, as a way of extending the service live of solar cells, there is an increasing demand for an improvement in the wet heat resistance and partial discharge voltage of solar cell backsheets and polyester films used therein (Patent Documents 1 and 2). Furthermore, as films to be used in mold-releasing applications, films having controlled height and number of productions (peaks) on the surface have been proposed (Patent Documents 3 and 4).